The compound Sn3F3PO4 is formed on the tooth surface when treated with stannous fluoride. We plan to study experimentally the rate of this reaction as the stannous, fluoride, and hydrogen ion concentrations are varied. These are the three primary reactants in this reaction (in addition to the tooth mineral). The time course of the reaction will be monitored by periodic analysis for solution calcium by atomic absorption spectrophotometry, and the solid phases that form will be identified by means of x-ray diffraction and by chemical analyses. A mathematical model based on simultaneous diffusion and chemical equilibria will be developed to aid in the experimental design as the project progresses and, ultimately, to provide a quantitative mathematical representation for the reaction. Such an approach will permit us to optimize the rate of this reaction, which can lead to a new therapeutic regimen regarding solution composition and the time and frequency of treatment. In addition, since the project will involve monitoring the nature and amount of the solid product(s), those conditions under which other compounds form, such as calcium fluoride and SnHPO4, will be determined. Since calcium fluoride forms on teeth treated with acidulated phosphate fluoride preparations, knowing those conditions whereby both Sn3F3PO4 and calcium fluoride form will permit us to design a drug delivery system that will indeed optimize the incorporation of fluoride on enamel by topical means.